Extending the cmake-based Current build.

[dkorolev]

Hi @mzhurovich !

• Extended curent_build.h to be auto-updated by each cmake-based build.
• #define-d C5T_CMAKE_PROJECT when built under cmake.

Keeping my inner nerd happy one commit at a time.

PS: As with the last cmake-related change, I've temporarily pointed the test script to my branch. Will flip back once this is merged.

[dkorolev]

Note to self. Local test run command:

rm -rf current_test_cmake/
mkdir -p current_test_cmake/a/b/c/d/e/f
(cd current_test_cmake/a/b/c/d/e/f; wget https://raw.githubusercontent.com/dkorolev/Current/current_build_autogen_header_for_cmake/cmake/Makefile)
(cd current_test_cmake/a/b/c/d/e/f; wget https://raw.githubusercontent.com/dkorolev/Current/current_build_autogen_header_for_cmake/cmake/CMakeLists.txt)
(cd current_test_cmake/a/b/c/d/e/f; wget https://raw.githubusercontent.com/dkorolev/Current/current_build_autogen_header_for_cmake/cmake/run-cmake-test.sh)
(cd current_test_cmake/a/b/c/d/e/f; chmod +x run-cmake-test.sh; ./run-cmake-test.sh)

[dkorolev]

TODO(dkorolev): Try this on Windows under Visual Studio too!